In present-day internal combustion engines it is common-place for hot exhaust gases to be introduced into an air inlet duct at various phases of engine operation according to the speed and load in order to reduce the pollution. The exhaust gases are introduced downstream of the “butterfly” housing in the case of gasoline engines and downstream of the “metering” housing in the case of diesel engines. In all cases, the recirculated gases have to spread uniformly into each cylinder of the engine concerned, because each cylinder has to receive the same amount of external fresh air and of exhaust gas.
Usually, the air inlet system of an internal combustion engine comprises an air inlet duct, of circular or some other cross section, and a multiple-outlet manifold which follows on from the air inlet duct and which guides the air toward the various cylinders. In this context, the problem is that of introducing the exhaust gases into the air inlet duct in such a way that these gases form a uniform mixture with the admitted air before they enter the manifold.
To this end, one solution already proposed by the Applicant, which has been the subject of a French patent application no. 06/09181 filed on Oct. 19, 2006 and published under the number 2907513 on Apr. 25 2008, is to introduce the exhaust gases tangentially into a tubular mixing nozzle positioned in the air inlet duct coaxially with the latter and with the inlet to the manifold. A configuration configuration such as this in theory allows the exhaust gases to mix with the fresh air quickly and therefore over a short path, creating a swirling vortex in the mixing nozzle and in the downstream part of the inlet duct just before the mixture enters the manifold, and does so while at the same time thermally insulating the recirculated hot gases with a layer of fresh air surrounding the swirling vortex.
This solution is simple and has proved effective and adequate in a great many applications, that is to say for numerous known configurations of inlet duct and inlet manifold. However, it does prove to be defective or insufficient for some duct and manifold geometries, as specified hereinafter.
Hence, in the case of an air inlet duct of circular cross section, and with a manifold of which the inlet and the plenum are also of circular cross section, the swirling vortex created by the tubular mixing nozzle is maintained in the plenum before it reaches the various branches of the manifold, thus ensuring uniform distribution of the mixture.
However, some inlet ducts are not of circular cross section but have an oblong cross section. In such cases, the swirling vortex leaving the tubular mixing nozzle is rapidly destroyed because it is not contained by an external envelope of circular cross section. The mixing of the exhaust gases with the air is therefore far less effective and less uniform, and the distribution to the engine cylinders, which is performed downstream of this point, may be adversely affected.
Similarly, some manifolds have a flattened inlet and a flattened plenum. In such cases, the jet of exhaust gas leaving the mixing nozzle no longer swirls like a vortex but has a tendency to “stick” to the wall of the manifold, on one side of this manifold or the other. An asymmetric phenomenon such as this obviously impairs the distribution of the mixture between the cylinders.
French patent application 2871530 provides, for the exhaust gas recirculation of an internal combustion engine, a dual intake of these gases, on each side of the air inlet duct. Two symmetrical gas streams are thus injected into the inlet duct, at two distinct points, these mutually opposing gas streams colliding with one another, thereby dissipating some of their energy before, in the inlet duct, forming two adjacent contrarotating swirling vortexes, that is to say vortexes that rotate in opposite directions to one another.
This known embodiment still has disadvantages:                By its very principle, it gives rise to a loss in kinetic energy of the recirculated gases at the point where the two swirling vortexes are created, even though these vortexes succeed in retaining a maximum amount of energy to reach the manifold.        The two swirling vortexes are not individually confined and guided and simply develop throughout the circular cross section of the inlet duct, coming into direct contact with the wall of the air inlet duct, which thus runs the risk of becoming excessively heated.        Following on from the above point, the solution of that document in question is not intended for inlet ducts of oblong or flattened cross section.        Finally, the need to have two injection orifices for the recirculated gases, and two separate pipes for carrying these gases as far as the two injection points, makes the structure and manufacture of the device more complicated.        